Method for assessing and managing sensor uncertainties in a virtual flow meter

Abstract

The present approach relates to establishing metrics for the computation of uncertainty boundaries for mean values for pressure and temperature drop error and mean values for mass flow error. Using such metric, sensor inaccuracies may be accounted for in the calibration and/or estimation processes of a virtual flow meter. For example, these values may be employed in the assessment of improvement in a calibration process of virtual flow meters, which will facilitate maintaining the accuracy of such virtual flow meters.

The invention claimed is: 
     
       1. A virtual flow meter, comprising:
 a processor-based controller configured to: 
 select or receive a selection of an operating point related to a given flow rate of a phase of a production fluid; 
 select or receive a selection of a nominal case; 
 based on the operating point and the nominal case, generate a calculated outlet pressure and a calculated outlet temperature at a segment of interest; 
 for each combination of a measured inlet pressure and associated error, a measured inlet temperature and associated error, a measured gas mass flow rate and associated error, a measured oil mass flow rate and associated error, and a measured water mass flow rate and associated error:
 derive an outlet pressure and an outlet temperature at the segment for each combination; 
 calculate an outlet pressure difference between the calculated outlet pressure for the nominal case and the outlet pressure calculated for each combination; and 
 calculate an outlet temperature difference between the calculated outlet temperature for the nominal case and the outlet temperature calculated for each combination; 
 
 determine the largest outlet pressure difference and the largest outlet temperature difference for the combinations; and 
 select the largest outlet pressure difference and the largest outlet temperature difference as uncertainties related to, respectively, the outlet pressure and outlet temperature calculated for the nominal case. 
 
     
     
       2. The virtual flow meter of  claim 1 , wherein the processor-based controller is further configured to calculate a pressure drop error by taking the difference of the calculated pressure drop and a measured pressure drop. 
     
     
       3. The virtual flow meter of  claim 2 , wherein the uncertainty associated with the pressure drop error is calculated by considering the propagation rule related to the difference and makes use of the uncertainties associated with the calculated pressure drop and measured pressure drop. 
     
     
       4. The virtual flow meter of  claim 2 , wherein the calculated pressure drop comprises the difference between the calculated outlet pressure and the measured inlet pressure. 
     
     
       5. The virtual flow meter of  claim 2 , wherein the measured pressure drop comprises the difference between an outlet pressure measurement and the measured inlet pressure. 
     
     
       6. The virtual flow meter of  claim 1 , wherein the processor-based controller is further configured to calculate a temperature drop error by taking the difference of the calculated temperature drop and a measured temperature drop. 
     
     
       7. The virtual flow meter of  claim 6 , wherein the uncertainty associated with the temperature drop error is calculated by considering the propagation rule related to the difference and makes use of the uncertainties associated with the calculated temperature drop and measured temperature drop. 
     
     
       8. The virtual flow meter of  claim 6 , wherein the calculated temperature drop comprises the difference between the calculated outlet temperature and the measured inlet temperature. 
     
     
       9. The virtual flow meter of  claim 6 , wherein the measured temperature drop comprises the difference between an outlet temperature measurement and the measured inlet temperature. 
     
     
       10. The virtual flow meter of  claim 1 , wherein the processor-based controller is further configured to tune the parameters of the virtual flow meter for the segment of interest based at least in part on the pressure and/or temperature drop errors and associated uncertainties. 
     
     
       11. A processor-based method for determining uncertainties associated with outlet temperature and outlet pressure of a segment of a fluid production network, comprising:
 selecting or receiving a selection of an operating point related to a given flow rate of a phase of a production fluid; 
 selecting or receiving a selection of a nominal case; 
 based on the operating point and the nominal case, generating a calculated outlet pressure and a calculated outlet temperature at a segment of interest; 
 for each combination of a measured inlet pressure and associated error, a measured inlet temperature and associated error, a measured gas mass flow rate and associated error, a measured oil mass flow rate and associated error, and a measured water mass flow rate and associated error:
 deriving an outlet pressure and an outlet temperature at the segment for each combination; 
 calculating an outlet pressure difference between the calculated outlet pressure for the nominal case and the outlet pressure calculated for each combination; and 
 calculating an outlet temperature difference between the calculated outlet temperature for the nominal case and the outlet temperature calculated for each combination; 
 
 determining the largest outlet pressure difference and the largest outlet temperature difference for the combinations; and 
 selecting the largest outlet pressure difference and the largest outlet temperature difference as uncertainties related to, respectively, the outlet pressure and outlet temperature calculated for the nominal case. 
 
     
     
       12. The method of  claim 11 , further comprising tuning the parameters of the virtual flow meter for the segment of interest based at least in part on the pressure and/or temperature drop errors and associated uncertainties. 
     
     
       13. The method of  claim 11 , further comprising:
 calculating a pressure drop error by taking the difference of the calculated pressure drop and a measured pressure drop. 
 
     
     
       14. The method of  claim 13 , wherein the uncertainty associated with the pressure drop error is calculated by considering the propagation rule related to the difference and makes use of the uncertainties associated with the calculated pressure drop and measured pressure drop. 
     
     
       15. The method of  claim 11 , further comprising:
 calculating a temperature drop error by taking the difference of the calculated temperature drop and a measured temperature drop. 
 
     
     
       16. The method of  claim 15 , wherein the uncertainty associated with the temperature drop error is calculated by considering the propagation rule related to the difference and makes use of the uncertainties associated with the calculated temperature drop and measured temperature drop. 
     
     
       17. A processor-based method for determining a pressure drop error for a segment of a fluid production network, comprising:
 determining a calculated pressure drop for the segment by taking the difference between a calculated outlet pressure for the segment corresponding to a nominal case, determined using a forward model and a measured inlet pressure for the segment; 
 determining a measured pressure drop for the segment by taking the difference between an outlet pressure measurement for the segment and the measured inlet pressure; 
 calculating a pressure drop error for the segment by taking the difference of the calculated pressure drop and the measured pressure drop; and 
 tuning a calibration process associated with a multiphase flow model using the pressure drop error and associated uncertainty for the segment. 
 
     
     
       18. A processor-based method for determining a temperature drop error for a segment of a fluid production network, comprising:
 determining a calculated temperature drop for the segment by taking the difference between a calculated outlet temperature for the segment corresponding to a nominal case, determined using a forward model and a measured inlet temperature for the segment; 
 determining a measured temperature drop for the segment by taking the difference between an outlet temperature measurement for the segment and the measured inlet temperature; 
 calculating a temperature drop error for the segment by taking the difference of the calculated temperature drop and the measured temperature drop; and 
 tuning a calibration process associated with a multiphase flow model using the temperature drop error and associated uncertainty for the segment.